Electric terminal modules of the generic type, along with additional electric and/or electronic terminal modules, are installed primarily in switching cabinets. The electric terminal modules are normally attached in the switching cabinet by latching them onto a top-hat rail, whereby they are preferably arranged directly next to each other. In order to cut costs, the operators of machinery and installations strive to utilize the available switching cabinet space as efficiently as possible and—to the greatest extent possible—to reduce the number of switching cabinets that have to be set up.
The manufacturers of electric terminal modules are paying heed to this trend and more and more often, they are providing the operators of machinery and installations with electric terminal modules that are increasingly narrow so that an ever-greater number of them can be installed in a switching cabinet. Thus, terminal modules with an overall width of less than 8 mm are already available on the market. The reduction of the overall width of the electric terminal modules means that the space available for the installation of populated printed circuit boards is also continuing to decrease. In an electric terminal module with an overall width of less than 8 mm, not only the thickness of a printed circuit board that is installed in the electric terminal module but also the overall height of the electronic components installed on the printed circuit board are likewise gaining ever-greater importance.
Many of the above-mentioned electric terminal modules offer users the possibility to select settings from outside of the housing, so that they can set or change an electric functions of the terminal module such as, for example, a time function. Thus, such electric terminal modules make it possible to set the time after which, for example, a switching operation should be actuated in an application. The term adjustment of a function of the electric terminal module should also be understood to mean the setting and/or adjusting of an electric and/or physical parameter of the function of the electric terminal module. Other electric functions and/or parameters that can be set include, for example, current values, voltage values, resistance values, value ranges of input and/or output variables, amplification factors, delay times, modes of operation and the like. Particularly in the case of safety-related applications, the electric terminal modules of the generic type provide safety-relevant functions such as, for example, the setting of a maximally permissible speed for a safely reduced speed of a motor that is connected to the electric terminal module. Moreover, the other functions can also include the setting of frequencies of signals that have to be emitted, the single-channel or multiple-channel processing of input signals connected to the electric terminal module, the selection of muting functions and/or protection ranges, the setting of safe modes of operation or other safety-related functions.
It is often the case that adjustable potentiometers, capacitors, inductors, operating mode switches or the like are used to change the function of an electric terminal module. However, components are also used in which the function of the electric terminal module is set contact-free, for instance, through the optical and/or inductive detection of the adjustment path or through the detection of a momentary relative and/or absolute position of the adjusting means. Such components are normally arranged on the assembled side of a printed circuit board.
The adjusting means themselves are, for the most part, configured as mechanical switches, dials, levers, pushbuttons or the like. Consequently, the adjusting means can be not only turned but also swiveled or switched.
Due to the limited installation space available in electric terminal modules of the generic type, primarily electrical components employing SMD technology are used, which are installed and soldered directly onto the printed circuit board without connection wires. Since such components are arranged on at least one side of a printed circuit board, they are adjusted perpendicular to the surface of the printed circuit board.
In electric terminal modules with an overall width of less than 8 mm, preferably less than or equal to 6.2 mm, an opening can be provided in one side of the terminal modules in order to adjust the components that are installed on the printed circuit board. The electrically adjustable components are adjusted by inserting a screwdriver through the opening that has been created in the side surface of the electric terminal module as well as into an opening that is provided in the electric component for adjusting its electric characteristic quantity and that is configured to receive, for example, the tip of a screwdriver. In the described arrangement of the adjustable electric component, the adjustment is only possible from one side of the terminal module. However, as a rule, an adjustment is no longer possible once several electric terminal modules are arranged directly next to each other.
Another solution is to provide a printed circuit board underneath a cover of an electric terminal module, whereby the adjustable electric component is arranged on said printed circuit board. In this case, the component is adjusted using a screwdriver through an opening that passes through the cover. However, such a configuration is not possible if there is no longer sufficient space available for the component and for the additional printed circuit board in the housing due to the limited overall width of the electric terminal module. In the case of overall widths of less than 8 mm, such a solution is no longer feasible. Moreover, in order to assemble such a terminal module, there is a need for an additional printed circuit board and for another work step in order to populate the terminal module. Both of these measures result in an undesired increase in the production costs.
Furthermore, it should be pointed out that the soldering points of the electric components employing SMD technology are hardly capable of adequately absorbing the forces that occur, for example, when a screwdriver is used to carry out the adjustment. Thus, it can easily happen that the components are over-twisted or are even broken away from the printed circuit board.
Therefore, in view of the small overall width of the electric terminal modules, it is most advantageous to arrange the adjustable electric components on the printed circuit board that is installed in the electric terminal module and to also permit an adjustment when several electric terminal modules are arranged next to each other when they are installed, especially on a top-hat rail.
Sometimes, a wheel can be installed on the adjustable electric components in such a way that the rim of the wheel extends partially over the front of the electric terminal module and can be operated from the outside. The component is positioned near the edge of a printed circuit board.
However, it is a drawback that the above-mentioned electric components such as potentiometers, adjustable capacitors and the like are structured as compact components that are closed towards the outside and that have soldering tags or connection legs on the outside for purposes of soldering such components onto a printed circuit board. Furthermore, such components are made up of numerous individual elements that are arranged on top of each other in several layers and that are installed together in a specially provided housing.
SMD components are normally attached to a printed circuit board by soldering at least one edge of the component housing to contact points on the printed circuit board. Consequently, as far as the available overall width is concerned, it is necessary to take into account not only the thickness of the printed circuit board but also the overall height of the electric component.
Conventional potentiometers, for example, are structured in such a way that resistance layers and at least one pick-off track are arranged on a carrier material, and a pick-up that creates an electric connection between both of them accesses said pick-off track. The entire arrangement is installed in its own housing. With this type of potentiometer, a wheel is additionally installed on the component and this wheel can be used, for example, to adjust the resistance value of a potentiometer. The same applies in an analogous manner for other adjustable electric components such as, for instance, adjustable capacitors such like variable capacitors and/or trimmers, adjustable inductors or else for adjustable electric components in which the change in the position of the wheel is determined optically, inductively and/or capacitively.
Moreover, by arranging a wheel on the adjustable electric component at a later point in time, the connecting points on the printed circuit board are covered, so that it is hardly or not at all possible to check the quality of the soldering points. This makes the search for flaws very difficult in case of flawed soldering points. Moreover, when the potentiometer with an attached wheel is soldered, the temperature is so high that the wheel, which is normally made of plastic, would be damaged. Since the overall height of such a potentiometer is already considerable, there would not be much space left for the rim of the wheel, thus making it difficult to adjust the wheel. Moreover, the rim can no longer be printed on.
All of the above-mentioned electric components themselves already have an overall height that—with the installation of a wheel and with the thickness of the printed circuit board—sometimes considerably exceeds the space available in electric terminal modules having an overall width of well below eight millimeters.
German patent application DE 1921230 A describes a potentiometer in which several resistance layers are installed on an insulating plate. A wiper is attached onto a shaft, and this shaft is mounted rotatably in a collar which, in turn, is secured in a bore of the insulating plate. The adjustment of the resistance value of the potentiometer is carried out by adjusting the shaft onto which a wiper is attached and whose end has a slit to receive the tip of a screwdriver. In addition, there are at least two washers that, together with the thickness of the insulating plate, further increase the overall height of the potentiometer. No additional electric components are arranged on the insulating plate. The described potentiometer is connected to additional components on a printed circuit board via soldering tags with mounting holes and/or soldering holes, so that the forces that occur when the potentiometer is adjusted have to be dissipated onto the printed circuit board exclusively through the soldering tags.
German patent application DE 2521789 A1 describes a potentiometer or slide resistor that is preferably provided as an individual building block for purposes of creating a direct, integral connection to a printed circuit board that has additional switching elements. For this purpose, resistance layers are applied onto the surface of the printed circuit board and these resistance layers are accessed by a pick-off that connects a pick-off track to resistance sliding tracks. The resistance value of the potentiometer can be changed by sliding the pick-off. Since the printed circuit board is perforated, a mounting part and a sliding or holding part are provided for guiding and attaching the component onto and/or into the circuit substrate. These parts are arranged on both sides of the perforated printed circuit board. The mounting part and the sliding or holding part on both sides of the surface of the printed circuit board increase the overall height of the potentiometer to such an extent that installation into electric terminal modules of the generic type is no longer possible.
An electric terminal module that already contains a printed circuit board with an adjustable electric component is described in German patent specification DE 43 08 242 C1. The adjustable electric component on the circuit substrate, the printed circuit board with the appertaining circuitry, the thumbwheel provided for adjusting the adjustable electric component arranged on the circuit substrate, and the appertaining covers are connected to each other before being installed and they are subsequently placed into the housing. In this approach as well, the overall height of the thumbwheel that is connected to the adjustable electric component also still has to be added to the overall height of the adjustable electric component. Its use in an electric terminal module with an even narrower overall width of less than eight millimeters is likewise no longer possible.